MicroProfile Context Propagation

    ManagedExecutor executor = ManagedExecutor.builder()
        .propagated(ThreadContext.APPLICATION)
        .cleared(ThreadContext.ALL_REMAINING)
        .maxAsync(5)
        .build();

    ThreadContext threadContext = ThreadContext.builder()
        .propagated(ThreadContext.APPLICATION, ThreadContext.CDI)
        .cleared(ThreadContext.ALL_REMAINING)
        .build();

    CompletableFuture<Long> stage = executor.newIncompleteFuture()
        .thenApply(function)
        .thenAccept(consumer);
    stage.completeAsync(supplier);

    threadContext.withContextCapture(unmanagedCompletionStage)
        .thenApply(function)
        .thenAccept(consumer);

    @Produces @ApplicationScoped @SecAndAppContextQualifier
    ManagedExecutor executor1 = ManagedExecutor.builder()
        .propagated(ThreadContext.SECURITY, ThreadContext.APPLICATION)
        .build();

    ... // in some other bean
    @Inject
    void setCompletableFuture(@SecAndAppContextQualifier ManagedExecutor executor2) {
        completableFuture = executor2.newIncompleteFuture();
    }

    ... // in yet another bean
    @Inject @SecAndAppContextQualifier
    ManagedExecutor executor3;

    // example qualifier annotation
    @Qualifier
    @Retention(RetentionPolicy.RUNTIME)
    @Target({ ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER })
    public @interface SecAndAppContextQualifier {}

mp.context.ManagedExecutor.propagated=Security,Application
mp.context.ManagedExecutor.cleared=Remaining
mp.context.ManagedExecutor.maxAsync=10
mp.context.ManagedExecutor.maxQueued=-1

mp.context.ThreadContext.propagated=None
mp.context.ThreadContext.cleared=Security,Transaction
mp.context.ThreadContext.unchanged=Remaining

import java.util.concurrent.CompletionStage;
import java.util.concurrent.CompletableFuture;
import javax.servlet.ServletConfig;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.eclipse.microprofile.context.ManagedExecutor;
import org.eclipse.microprofile.context.ThreadContext;

public class ExampleServlet extends HttpServlet {
    ManagedExecutor executor;

    public void init(ServletConfig config) {
        executor = ManagedExecutor.builder()
                                  .propagated(ThreadContext.APPLICATION)
                                  .cleared(ThreadContext.ALL_REMAINING)
                                  .maxAsync(5)
                                  .build();
    }

    public void doGet(HttpServletRequest req, HttpServletResponse res) {
       completionStage = executor.runAsync(task1)
                             .thenRunAsync(task2)
                             ...
    }

    public void destroy() {
        executor.shutdown();
    }
}

import java.util.concurrent.CompletableFuture;
import java.util.function.Function;
import java.util.function.Supplier;
import javax.servlet.ServletConfig;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.eclipse.microprofile.context.ThreadContext;

public class ExampleServlet extends HttpServlet {
    ThreadContext threadContext;

    public void init(ServletConfig config) {
        threadContext = ThreadContext.builder()
                            .propagated(ThreadContext.APPLICATION, ThreadContext.SECURITY)
                            .unchanged()
                            .cleared(ThreadContext.ALL_REMAINING)
                            .build();
    }

    public void doGet(HttpServletRequest req, HttpServletResponse res) {
        Function<Long, Long> contextFn = threadContext.contextualFunction(x -> {
            ... operation that requires security & application context
            return result;
        });

        // By using java.util.concurrent.CompletableFuture.supplyAsync rather
        // than a managed executor, context propagation is unpredictable,
        // except for the contextFn action that we pre-contextualized using
        // ThreadContext above.
        stage = CompletableFuture.supplyAsync(supplier)
                                 .thenApplyAsync(function1)
                                 .thenApply(contextFn)
                                 ...
    }
}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import javax.inject.Qualifier;

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER })
public @interface SecurityAndCDIContext {}

import org.eclipse.microprofile.context.ManagedExecutor;
import org.eclipse.microprofile.context.ThreadContext;
import javax.enterprise.context.ApplicationScoped;
import javax.enterprise.inject.Produces;

@ApplicationScoped
public class MyFirstBean {
    @Produces @ApplicationScoped @SecurityAndCDIContext
    ManagedExecutor executor = ManagedExecutor.builder()
        .propagated(ThreadContext.SECURITY, ThreadContext.CDI)
        .build();

    void disposeExecutor(@Disposes @SecurityAndCDIContext ManagedExecutor exec) {
        exec.shutdownNow();
    }
}

import org.eclipse.microprofile.context.ManagedExecutor;
import javax.enterprise.context.ApplicationScoped;
import javax.inject.Inject;

@ApplicationScoped
public class MySecondBean {
    @Inject @SecurityAndCDIContext
    ManagedExecutor sameExecutor;
    ...
}

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import javax.inject.Qualifier;

@Qualifier
@Retention(RetentionPolicy.RUNTIME)
@Target({ ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER })
public @interface AppContext {}

import org.eclipse.microprofile.context.ThreadContext;
import javax.enterprise.context.ApplicationScoped;
import javax.enterprise.inject.Produces;

@ApplicationScoped
public class MyFirstBean {
    @Produces @ApplicationScoped @AppContext
    createAppContextPropagator() {
        return ThreadContext.builder()
               .propagated(ThreadContext.APPLICATION)
               .cleared(ThreadContext.SECURITY, ThreadContext.TRANSACTION)
               .unchanged(ThreadContext.ALL_REMAINING)
               .build();
  }
}

import org.eclipse.microprofile.context.ThreadContext;
import javax.enterprise.context.ApplicationScoped;
import javax.inject.Inject;
...

@ApplicationScoped
public class MySecondBean {
    Function<Integer, Item> findItem;

    @Inject
    protected void setFindItem(@AppContext ThreadContext appContext) {
        findItem = appContext.contextualFunction(i -> {
            try (Connection con =
                 ((DataSource) InitialContext.doLookup("java:comp/env/ds1")).getConnection();
                 PreparedStatement stmt = con.prepareStatement(sql)) {
                stmt.setInt(1, i);
                return toItem(stmt.executeQuery());
            } catch (Exception x) {
                throw new CompletionException(x);
            }
        });
    }
    ...
}

executor = ManagedExecutor.builder()
                          .propagated(ThreadContext.TRANSACTION)
                          .cleared(ThreadContext.ALL_REMAINING)
                          .build(); // <-- raises IllegalStateException

executor = ManagedExecutor.builder()
           .propagated(ThreadContext.TRANSACTION, ThreadContext.APPLICATION)
           .cleared(ThreadContext.ALL_REMAINING)
           .build();

// propagates the absence of a transaction,
// allowing the action to start its own transaction
stage1 = executor.supplyAsync(supplier);
stage2 = stage1.thenApply(u -> {
    try {
        DataSource ds = InitialContext.doLookup("java:comp/env/ds1");
        UserTransaction tx = InitialContext.doLookup("java:comp/UserTransaction");
        tx.begin();
        try (Connection con = ds.getConnection()) {
            return u + con.createStatement().executeUpdate(sql);
        } finally {
            tx.commit();
        }
    } catch (Exception x) {
        throw new CompletionException(x);
    }
});

tx.begin();
... do transactional work here

updateCount = stage2.join(); // <-- stage2's action is guaranteed to never
                             //     run under this transaction because absence
                             //     of a transaction is propagated to it

... more transactional work

tx.begin();
stage = executor.runAsync(action); // <-- raises IllegalStateException
...

executor = ManagedExecutor.builder()
           .propagated(ThreadContext.TRANSACTION)
           .build();

// Allowed because it limits the transaction to serial use
stage1 = executor.newIncompleteFuture();
tx.begin();
try {
    stage3 = stage1.thenApply(updateCount -> {
        try (Connection con = dataSource.getConnection()) {
            return updateCount + con.createStatement().executeUpdate(sql2);
        } catch (SQLException x) {
            throw new CompletionException(x);
        }
    }).thenApply(updateCount -> {
        try (Connection con = dataSource.getConnection()) {
            return updateCount + con.createStatement().executeUpdate(sql3);
        } catch (SQLException x) {
            throw new CompletionException(x);
        }
    }).whenComplete((result, failure) -> {
        try {
            if (failure == null && tx.getStatus() == Status.STATUS_ACTIVE)
                tx.commit();
            else
                tx.rollback();
        } catch (Exception x) {
            if (failure == null)
                throw new CompletionException(x);
        }
    });
} finally {
    // vendor-specific means required to obtain TransactionManager instance
    transactionManager.suspend();
}

// ... possibly on another thread
stage1.complete(initialCount);

tx.begin();
try {
    stage = executor.supplyAsync(() -> {
        try (Connection con = dataSource.getConnection()) {
            return con.createStatement().executeUpdate(sql1);
        } catch (SQLException) {
            throw new CompletionException(x);
        }
    });

    try (Connection con = dataSource.getConnection()) {
        con.createStatement().executeUpdate(sql2);
    });

    stage.join(); // <-- raises CompletionException with a chained
                  //     IllegalStateException indicating lack of support
                  //     for propagating an active transaction to multiple
                  //     threads

    tx.commit();
} catch (Exception x) {
    tx.rollback();
    ...

tx.begin();
try {
    stage1 = executor.runAsync(action1);
    stage2 = executor.runAsync(action2);
    stage3 = stage1.runAfterBoth(stage2, (u,v) -> action3)
                   .whenComplete((result, failure) -> {
        try {
            if (failure == null && tx.getStatus() == Status.STATUS_ACTIVE)
                tx.commit();   // <-- raises SystemException if unsupported within dependent stage
            else
                tx.rollback(); // <-- raises SystemException if unsupported within dependent stage
        } catch (Exception x) {
            if (failure == null)
                throw new CompletionException(x);
        }
    });
} finally {
    // vendor-specific means required to obtain TransactionManager instance
    transactionManager.suspend();
}

tx.begin();
try {
    stage1 = executor.runAsync(action1);
    stage2 = executor.runAsync(action2);
    stage3 = CompletableFuture.allOf(stage1, stage2);
    stage3.join();
} finally {
    if (tx.getStatus() == Status.STATUS_ACTIVE && !stage3.isCompletedExceptionally())
        tx.commit();
    else
        tx.rollback();
}

    executor = ManagedExecutor.builder()
                   .cleared(ThreadContext.TRANSACTION, ThreadContext.SECURITY)
                   .propagated(ThreadContext.ALL_REMAINING)
                   .build();

    CompletableFuture<Long> stage1 = executor.newIncompleteFuture();
    stage1.thenApply(function1)      // runs with captured context
          .thenApply(function2);     // runs with captured context
    stage1.completeAsync(supplier1); // runs with captured context

    threadContext = ThreadContext.builder()
                        .propagated(ThreadContext.SECURITY)
                        .unchanged()
                        .cleared(ThreadContext.ALL_REMAINING)
                        .build();

    stage = threadContext.withContextCapture(invokeSomeMethodThatReturnsUnmanagedCompletionStage());
    stage.thenApply(function1)  // runs with captured context
         .thenAccept(consumer); // runs with captured context

    threadContext = ThreadContext.builder()
                        .propagated(ThreadContext.SECURITY)
                        .unchanged()
                        .cleared(ThreadContext.ALL_REMAINING)
                        .build();

    Consumer<String> contextualConsumer = threadContext.contextualConsumer(s -> {
            ... do something that requires context
        });

    stage = invokeSomeMethodThatReturnsUnmanagedCompletionStage();
    stage.thenApply(function1)            // context is unpredictable
         .thenAccept(contextualConsumer); // runs with captured context

    threadContext = ThreadContext.builder()
                                 .cleared(ThreadContext.TRANSACTION)
                                 .unchanged(ThreadContext.SECURITY)
                                 .propagated(ThreadContext.ALL_REMAINING)
                                 .build();
    contextSnapshot = threadContext.currentContextExecutor();

    ... on some other thread,
    contextSnapshot.execute(() -> {
        ... do something that requires the previously captured context
    });

    threadContext = ThreadContext.builder()
                        .propagated(ThreadContext.APPLICATION)
                        .unchanged(ThreadContext.TRANSACTION)
                        .cleared(ThreadContext.ALL_REMAINING)
                        .build();

    Callable<Integer> updateDatabase = threadContext.contextualCallable(() -> {
        DataSource ds = InitialContext.doLookup("java:comp/env/ds1");
        try (Connection con = ds.getConnection()) {
            return con.createStatement().executeUpdate(sql);
        }
    }));

    ... on some other thread,

    tx.begin();
    ... do transactional work
    // runs as part of the transaction, but with the captured application scope
    updateDatabase.call();
    ... more transactional work
    tx.commit();

META-INF/services/org.eclipse.microprofile.context.spi.ContextManagerExtension